Chemical mechanical process (CMP) has become a widely used technique for polishing certain work pieces. Particularly, the computer manufacturing industry has begun to rely heavily on CMP processes for polishing wafers of ceramics, silicon, glass, quartz, metals, and mixtures thereof for use in semiconductor fabrication. Such polishing processes generally entail applying the wafer against a rotating pad made from a durable organic substance such as polyurethane. To the pad is added a chemical slurry containing a chemical solution capable of breaking down the wafer substance and an amount of abrasive particles which act to physically erode the wafer surface. The slurry is continually added to the spinning CMP pad, and the dual chemical and mechanical forces exerted on the wafer cause it to be polished in a desired manner.
Of particular importance to the quality of polishing achieved, is the distribution of the abrasive particles throughout the pad. The top of the pad holds the particles, usually by a mechanism such as fibers, or small pores, which provide a friction force sufficient to prevent the particles from being thrown off of the pad due to the centrifugal force exerted by the pad's spinning motion. Therefore, it is important to keep the top of the pad as flexible as possible, and to keep the fibers as erect as possible, or to assure that there are an abundance of openings and pores available to receive new abrasive particles.
A problem with maintaining the top of the pad is caused by an accumulation of polishing debris coming from the work piece, abrasive slurry, and dressing disk. This accumulation causes a “glazing” or hardening of the top of the pad that mats the fibers down, thus making the pad less able to hold the abrasive particles of the slurry, and thus significantly decreases the pad's overall polishing performance. Further, with many pads the pores used to hold the slurry become clogged, and the overall asperity of the pad's polishing surface becomes depressed and matted. Therefore, attempts have been made to revive the top of the pad by “combing” or “cutting” it with various devices. This process has come to be known as “dressing” or “conditioning” the CMP pad. Many types of devices and processes have been used for this purpose. One such device is a disk with a plurality of super hard crystalline particles, such as diamond particles attached to a surface, or substrate thereof.
Yet another disadvantage with modern CMP pad dressers is reduced life of the pad conditioner and CMP pad. As noted, abrasive particles and CMP pads can wear out prematurely when the particles cut too deeply into the pad and consume the pad unnecessarily. Such premature wear reduces the ability of the CMP pad dresser to effectively polish the work piece. When functioning optimally, the abrasive particles act to refurbish the asperities in the CMP pad, and thus create an optimal polishing environment.
The rate at which a CMP pad is dressed may affect the surface roughness of the pad, which in turn may determine the amount of slurry held on the surface and thus affect polishing rate. In general, the polishing rate of the wafer is proportional to the dressing rate. However, if the dressing rate is excessive, the pad surface may become overly rough, and thus decrease the uniformity of the polished wafer. As such, optimizing the dressing rate may improve polishing rate without adversely affecting the quality of the wafer.
In view of the foregoing, it is desirable to obtain CMP pad dressers and methods configured to control dresser performance in order to achieve optimal dressing results, with maximized efficiency and lifespan for various applications.